This application claims the priority of German Patent Document 100 35 762.8, filed in Germany, Jul. 22, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an exhaust-gas turbocharger for an internal combustion engine and a method of operating an exhaust-gas turbocharger. Preferred embodiments of the invention relate to an exhaust-gas turbocharger for an internal combustion engine, having an exhaust-gas turbine which is provided with variable turbine geometry for variable setting of an effective flow inlet cross section to a turbine wheel, and having a compressor which is connected to the exhaust-gas turbine via a shaft, the variable turbine geometry being adjustable by a regulating device between a closed position reducing the flow inlet cross section and an open position widening the flow inlet cross section.
Preferred embodiments of the invention also relate to a method of operating an exhaust-gas turbocharger for an internal combustion engine which is provided with a variable turbine geometry which can be set in a variable manner and can be adjusted as a function of characteristic quantities of the exhaust-gas turbocharger and/or of the internal combustion engine between a closed position reducing a flow inlet cross section to the turbine wheel and an open position widening the flow inlet cross section.
Described in German Patent Publication DE 197 27 141 C1 is a supercharged internal combustion engine having an exhaust-gas turbocharger which is provided with variable turbine geometry for the variable setting of the effective flow inlet cross section to the turbine wheel. By the adjustment of the variable turbine geometry, the exhaust-gas backpressure in the piping between cylinder outlet of the internal combustion engine and turbine inlet can be influenced and the power requirement of the turbine and also the compressor output and therefore also the charge pressure can be set in a variable manner. The variable turbine geometry consists of a guide cascade ring having adjustable guide blades which can be adjusted between a closed position with minimum flow inlet cross section and an open position with maximum flow inlet cross section. As a function of the state of the internal combustion engine, the guide blades are adjusted by means of an actuator in such a way that the desired charge pressure and the desired exhaust-gas backpressure are set.
Such turbochargers with variable turbine geometry can also be used in engine braking operation. In engine braking operation, the guide cascade is shifted into the closed position, in which the flow inlet cross section to the turbine wheel is markedly reduced, whereupon an increased exhaust-gas backpressure builds up in the piping section between cylinder outlet and turbine inlet, this increased exhaust-gas backpressure causing exhaust gas to flow at high velocity through the open flow passages between the guide blades and act upon the turbine wheel with a high impulse. An increased charge pressure is thereupon produced on the intake side, and the air compressed in the cylinders is released into the exhaust-gas line via braking valves. In engine braking operation, therefore, the piston, in the compression and exhaust stroke, must perform compression work against the high exhaust-gas backpressure in the exhaust-gas line.
In such exhaust-gas turbochargers, wear may occur in particular after a prolonged operating period, and this wear may result in the desired closed position of the guide cascade no longer being reached, with the result that the desired level of the exhaust-gas backpressure and of the charge pressure is no longer reached. In engine braking operation, the maximum engine braking power can then no longer be achieved.
An object of the invention is to solve the problem of compensating for wear in exhaust-gas turbochargers having variable turbine geometry with simple measures.
According to certain preferred embodiments of the invention this problem is solved by providing an exhaust-gas turbocharger for an internal combustion engine, having an exhaust-gas turbine which is provided with variable turbine geometry for variable setting of an effective flow inlet cross section to a turbine wheel, and having a compressor which is connected to the exhaust-gas turbine via a shaft, the variable turbine geometry being adjustable by a regulating device between a closed position reducing the flow inlet cross section and an open position widening the flow inlet cross section, wherein a variable stop limiting an end position of the variable turbine geometry is provided, and wherein the position of the stop can be set in a variable manner.
According to certain preferred embodiments of the invention this problem is solved by providing a method of operating an exhaust-gas turbocharger for an internal combustion engine which is provided with a variable turbine geometry which can be set in a variable manner and can be adjusted as a function of characteristic quantities of the exhaust-gas turbocharger and/or of the internal combustion engine between a closed position reducing a flow inlet cross section to the turbine wheel and an open position widening the flow inlet cross section, wherein at least one of the closed and opened positions of the turbine geometry is set in a variable manner as a function of the characteristic quantities.
According to the invention, a stop is provided in the exhaust-gas turbocharger having variable turbine geometry, this stop limiting an end position of the variable turbine geometry, it being possible for the position of the stop to be set in a variable manner. Via the setting of the stop position, in particular the end closed position, but if need be also the end open position, of the variable turbine geometry can be reset and limited to a desired value. If the variable turbine geometry can no longer reach, for example, the desired closed position on account of wear and the turbine geometry remains in an open state, a new end position for the variable turbine geometry can be preset by varying the position of the closing stop, in which end position the turbine geometry can again assume the desired position. In this way, in particular wear-related play in the joints and bearing arrangements of the turbine geometry can be compensated for.
The closing stop may be provided either directly on a component of the turbine geometry or else on a regulating device, via which the variable turbine geometry can be adjusted between the open and closed positions.
In an expedient development of certain preferred embodiments of the invention, a measuring device is provided for measuring a characteristic quantity which characterizes the behavior of the turbine, the characteristic quantity being used as a measure of the requisite adjustment of the closing stop and/or opening stop. The characteristic quantity measured may be, for example, the charge pressure in the closed position of the variable turbine geometry. The stop is then adjusted until the measured characteristic quantity coincides with a predetermined desired value which must be obtained in the relevant position of the turbine geometry. The measurement and setting are advantageously carried out in engine braking operation. However, it is also advantageous to carry out the measurement and setting in the fired drive operating mode according to certain contemplated preferred embodiments of the invention.
In addition to the closing stop limiting the closed position, an opening stop limiting the open position is also advantageously provided in certain preferred embodiments of the invention. It is then possible for this opening stop to be adjusted like the closing stop in a corresponding manner, so that both end positions of the variable turbine geometry can be set in a variable manner. The opening stop is intended in particular to ensure that, when using a guide cascade ring having adjustable guide blades, the maximum open position of the guide blades is limited in order to ensure that the blade edges maintain a sufficiently large distance from the turbine wheel in the open position.
In preferred embodiments of the method according to the invention for operating the exhaust-gas turbocharger having variable turbine geometry, the end positions of the turbine geometry are set in a variable manner as a function of measured characteristic quantities of the supercharger or of the internal combustion engine. In this case, the setting, if desired, may be effected automatically by appropriate actuating elements which are acted upon by a control device in which actuating signals acting upon the actuating elements are produced as a function of the measured variables, which are processed according to a predetermined relationship.
In order to be able to introduce compensating measures even before damage occurs or before the supercharger effect decreases, it is expedient according to certain preferred embodiments of the invention to determine a wear factor which corresponds to the number of actuations of the variable turbine geometry. In this case, the actions of the movement of the variable turbine geometry, the blade movements in the case of a guide cascade having adjustable guide blades, in the various operating states of the internal combustion engine, namely fired drive operating mode and engine braking operation, are continuously counted and used as an indication of the current wear state. If the wear factor reaches a certain value, either one or both end positions of the turbine geometry can be reset automatically or the resetting is effected during a maintenance interval. The wear factor is advantageously stored in a control device or indicated in an indicating device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.